Mask stripper for electroform parting

ABSTRACT

A method for separating an electroformed article from a mandrel comprising: (a) masking a portion of a mandrel with a mask comprising an electrically nonconductive outer surface; (b) electroforming an article on the mandrel wherein the electroforming material is deposited on the mandrel surface but fails to adhere to the nonconductive outer surface of the mask, whereby the end of the electroformed article is adjacent to the mask; and (c) removing the article from the mandrel by either: (i) pushing the mask against the end of the article to effect movement of the article in the direction of separation; or (ii) removing the mandrel while keeping the mask stationary, whereby the end of the article pushes against the mask during withdrawal of the mandrel.

This invention relates generally to methods for separating anelectroform component from a mandrel, and more particularly to methodsemploying a mask which also can be used as a provider of a force such asan axial force to initiate movement to the electroform and to move theelectroform axially until it is stripped from the mandrel or until themandrel is stripped from the electroform. The removed electroformedarticle may be used for example as a substrate in the fabrication ofphotoreceptors.

Parting of the electroform from the mandrel typically occurs by handwith the worker gripping the central portion of the elctroform duringparting. This is disadvantageous since one or more of the following mayoccur: contamination of the electroform surface such as by dirty orcontaminated gloves; marring the finish (matte finish is typicallyemployed to eliminate the plywood phenomenon); scratching or denting theelectroform surface; rendering parting more difficult by gripping theelectroform which reduces any parting gap between the electroform andthe mandrel; and physical damage to the mandrel. There is a need for newseparation methods which reduce or eliminate one or more of the abovedescribed problems, and this need is met by the present invention.

The use of nonconductive masks to block deposition on parts of a mandrelduring electroforming is known. However, the use of a mask infacilitating electroform parting appears to be unknown.

The following documents may be of interest:

Herbert et al., U.S. Pat. No. 4,902,386, discloses a mandrel having anellipsoid shaped end.

Herbert, U.S. Pat. No. 4,501,646, discloses an electroforming processwhich effects a parting gap by heating or cooling.

Petropoulous et al., U.S. Pat. No. 5,021,109, discloses devices andmethods to facilitate removal of a tubular sleeve from a mandrel,reference for example, col. 11.

Melnyk et al., U.S. Pat. No. 5,064,509, discloses devices and methods tofacilitate removal of an electroformed article from a mandrel,reference, cols. 12-13.

McAneney et al., U.S. Pat. No. 4,711,833, discloses air assisted removalof substrates from a mandrel, reference for example, col. 10, lines30-40.

Kenworthy et al., U.S. Pat. No. 4,549,939, discloses the removal of anelectroformed part from a photomask mandrel by a variety of ways,reference, for example, col. 3.

Herbert et al., U.S. Pat. 4,781,799, discloses an elongatedelectroforming mandrel, the mandrel comprising at least a first segmenthaving at least one mating end and a second segment having at least onemating end, the mating end of the first segment being adapted to matewith the mating end of the second segment.

Melnyk et al., U.S. Pat. No. 5,160,421, discloses the use of anonconductive coating to block deposition on a portion of a mandrel,reference for example, col. 3, lines 43-48.

Luch et al., U.S. Pat. No. 4,158,612, discloses a polymeric mandrel forelectroforming and a method of electroforming.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide methods forseparating the electroform from the mandrel by employing a mask tocontrol the terminus of deposition of material during electroforming andto use the mask as a stripper.

It is a further object in embodiments to select materials for themandrel and the electroformed article having similar or differentcoefficients of expansion.

It is another object in embodiments to employ electroform partingmethods which reduce or eliminate one or more of the following:contamination of the electroform surface such as by dirty orcontaminated gloves; marring the finish (matte finish is typicallyemployed to eliminate the plywood phenomenon); scratching or denting theelectroform surface; making parting more difficult by gripping theelectroform which reduces any parting gap between the electroform andthe mandrel; and physical damage to the mandrel.

These objects and others are accomplished in embodiments by a method forseparating an electroformed article from a mandrel comprising: (a)masking a portion of a mandrel with a mask comprising an electricallynonconductive outer surface; (b) electroforming an article on themandrel wherein the electroforming material is deposited on the mandrelsurface and substantially fails to adhere to or does not adhere to thenonconductive outer surface of the mask, whereby the end of theelectroformed article is adjacent to the mask; and (c) removing thearticle from the mandrel by: (i) pushing the mask against the end of thearticle to effect movement of the article in the direction ofseparation; or (ii) removing the mandrel while keeping or retaining themask stationary, whereby the end of the article pushes against the maskduring withdrawal of the mandrel.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects of the present invention will become apparent as thefollowing description proceeds and upon reference to the Figures, whichrepresent preferred embodiments:

FIGS. 1(a) and (b) are schematic illustrations of one method to separatean electroform from the mandrel.

FIGS. 2(a) and (b) are schematic illustrations of another method toseparate an electroform from the mandrel.

DETAILED DESCRIPTION

In FIG. 1(a), mask 5 is positioned at the top of mandrel 10. Electroform20 is deposited by electroforming on mandrel 10 but no electroformingmaterial is deposited on mask 5 due to its electrically nonconductiveouter surface. Mandrel 10 is fixedly coupled to support 15. In FIG.1(b), electroform 20 is separated from mandrel 10 by pushing mask 5against the end of electroform 20 and maintaining a force against theend thereof. Once the "sticking force" is overcome between theelectroform and mandrel, the electroform is pushed off the mandrel bythe mask. The force employed to push the mask against the electroformand to move the mask and electroform may be manual force or the forcemay be supplied by any suitable mechanical apparatus including grippingdevices and motors. The mandrel and the support typically remainstationary during parting of the electroform.

In FIG. 2(a), mask 5 is positioned at the top of mandrel 10. Electroform20 is deposited on mandrel 10 but no material is deposited on mask 5 dueto its electrically nonconductive outer surface. Mandrel 10 isreleasably coupled to support 15. In FIG. 2(b), electroform 20 isseparated from mandrel 10 by pulling mandrel 10 out, whereby the end ofelectroform 20 pushes against the mask during withdrawal of the mandrel.Mask 5 is kept stationary by its presence adjacent to support 15. Oncethe "sticking force" is overcome between the electroform and mandrel,the electroform progresses off the mandrel as the mandrel is beingwithdrawn. The force employed in pulling out the mandrel may be manualforce or the force may be supplied by any suitable mechanical apparatusincluding gripping devices and motors. In a preferred embodiment, theapparatus to pull out the mandrel may be a threaded device that engagesthe end or the outer surface of the mandrel to apply axial force formandrel removal, wherein the end or the outer surface of the mandrel maybe grooved or threaded to engage the device.

In FIGS. 1 and 2, the support provides a handling apparatus of theassembly for immersion into the electroforming bath, a means totransport the assembly from the electroforming bath to a remote partingstation for electroform removal, and/or to provide electrical continuityto the mandrel. The support may be coupled to the mandrel by anysuitable technique. In embodiments, coupling between the mandrel andsupport is accomplished by one or more of the following: threadedconnection; interference or press fit; and slipfit and fastening screws,either from the end or sides of the support or both.

In FIGS. 1 and 2, an optional electrically nonconductive bottom mask,positioned at the parabolic or ellipsoid shaped end of the mandrel, maybe employed to control the bottom terminus of deposition of materialduring electroforming in combination with the top mask. In embodiments,the bottom mask may be removed and the separation proceeding asdescribed herein for FIGS. 1 and 2 where the top mask functions as thestripper. In a modification of FIG. 1 where the top mask is removed andthe mandrel is detached from the support, the bottom mask functions asthe stripper in a manner similar to the top mask by pushing against theelectroform end and forcing the electroform off the mandrel. Inembodiments, the bottom mask may have the same configuration andcomposition as the top mask.

In FIGS. 1 and 2, contact such as by gripping is preferably made onlywith the mask, the support, or both mask and support but not theelectroform surface. This is to reduce or eliminate one or more of thefollowing: contamination of the electroform surface such as by dirtygloves; marring the finish (matte finish is typically employed toeliminate the plywood phenomenon); scratching or denting the electroformsurface; and making parting more difficult by gripping the electroformwhich reduces any parting gap between the electroform and the mandrel.In addition, the present invention in embodiments may reduce thepossibility of physical damage to the mandrel since contact with themandrel surface is minimized. After the electroform is stripped off themandrel, the electroform progresses to the next operational step and themask and mandrel may be reassembled, inspected and reassembled, orcleaned and reassembled, or otherwise prepared and reassembled and thenre-inserted into the electroform bath and additional electroforms may bemade.

The mask may be fabricated from any suitable material or materials in asingle layer or multilayer design (two or more layers) wherein the maskhas an electrically nonconductive outer surface and an inner surfacecapable of engaging in sliding movement with the mandrel surface. In asingle layer design, the mask may be entirely fabricated of electricallynonconductive material. In a mask having two or more layers, the toplayer may be nonconductive and the other layer or layers may befabricated from a conductive material (e.g., metal or a polymericmaterial impregnated with a conductive material) or from the same ordifferent nonconductive material as that selected for the top layer. Ina mask having two or more layers, each layer may be of an effectivethickness, preferably ranging from about 0.5 mm to about 2 cm, and morepreferably ranging from about 1 mm to about 1 cm. Illustrative maskmaterials include thermoplastic and thermosetting resins such as rigidpolymers (e.g., polyethylene, polypropylene polyvinyl chloride,polymethyl methacrylate, fluoroplastics, ionomers, acrylonitrilebutadiene styrene), copolymers (e.g., ethylenepropylene,vinylchloride-acetate, vinylidene chloride-vinylchloride), compoundedmaterials (e.g., polyvinyl chloride plus acrylonitrile butadienestyrene), some elastomers (e.g., ethylene-propylene rubber), and epoxideresins (e.g., diglycidyl ether of bisphenol A (epoxy resin) withdicyandiamide hardener). Other suitable materials include wax. Inembodiments, the mask is elastic. A preferred mask material is butylrubber.

The mask material is selected from the materials disclosed herein suchthat the mandrel surface and the mask inner surface exhibit acoefficient of static friction effective for sliding movementtherebetween, preferably ranging from about 0.05 to about 1, and morepreferably 0.05 to about 0.50. Preferably, the mask does not buckle orcrimp when it is pushed against the electroform end or when theelectroform end presses against the mask edge.

The mask may have any suitable shape and dimensions: preferably a sleevelike band or collar; a thickness preferably ranging from about 1 mm toabout 3 cm, and more preferably about 2 mm to about 1 cm; a lengthpreferably ranging from about 5 mm to about 10 cm, and more preferablyabout 10 mm to about 5 cm. The mask is designed to snugly fit around themandrel circumference and thus the inside diameter of the maskcorresponds approximately to the outside diameter of the mandrel. Themask may have any effective diameter and preferably has an insidediameter, before positioning on the mandrel, ranging from about 3 cm toabout 20 cm, and more preferably from about 5 cm to about 10 cm.

In embodiments, an optional effective parting gap may be created betweena portion of the electroform and the mandrel to facilitate separation.Preferably, the parting gap ranges from about 0.1 mm to about 1 cm, andmore preferably from about 0.1 mm to about 5 mm in width separating theelectroform and the mandrel. The parting gap may be created by anysuitable method including reliance on differences in the coefficients ofthermal expansion between the mandrel and the article. Processes tocreate a parting gap are illustrated in Bailey et al., U.S. Pat. No.3,844,906 and Herbert, U.S. Pat. No. 4,501,646, the disclosures of whichare totally incorporated by reference.

The mandrel may have any effective design, and may be hollow or solid.The mandrel may have any effective cross-sectional shape such ascylindrical, oval, square, rectangular, or triangular. In embodiments,the mandrel has tapered sides. A preferred mandrel has an ellipsoid orparabolic shaped end, with the mandrel profite preferably like thatillustrated in Herbert et al., U.S. Pat. No. 4,902,386, the disclosureof which is totally incorporated by reference. Such a mandrel with anellipsoid or parabolic shaped end is preferred since the resultingelectroform will have a corresponding ellipsoid or parabolic shaped endwhich provides a gripping surface. Any damage to the ellipsoid orparabolic shaped end of the electroform during parting is generally ofno consequence since the end may be discarded, such as by cutting off,in the processing of photoreceptor substrates. The top end of themandrel may be open or closed, flat or of any other suitable design. Themandrel may be of any suitable dimensions. For example, the mandrel mayhave a length ranging from about 5 cm to about 100 cm; and an outsidediameter ranging from about 5 cm to about 30 cm. The mandrel may befabricated from any suitable material, preferably a metal such asaluminum, nickel, steel, iron, copper, and the like.

An optional hole or slight depression at the end of the mandrel isdesirable to function as a bleeding hole to facilitate more rapidremoval of the electroformed article from the mandrel. The bleed holeprevents the deposition of metal at the apex of the tapered end of themandrel during the electroforming process so that ambient air may enterthe space between the mandrel and the electroformed article duringremoval of the article subsequent to electroforming. The bleed holeshould have sufficient depth and circumference to prevent hole blockingdeposition of metal during electroforming. For a small diameter mandrelhaving an outside diameter between about 1/16 inch (0.2 mm) and about2.5 inches (63.5 mm) a typical dimension for bleed hole depth rangesfrom about 3 mm to about 14 mm and a typical dimension for circumferenceranges from about 5 mm and about 15 mm. Other mandrel diameters such asthose greater than about 63.5 mm may also utilize suitable bleed holeshaving dimensions within and outside these depth and circumferenceranges.

The mandrel may be optionally plated with a protective coating. Theplated coating is generally continuous except for areas that are maskedor to be masked and may be of any suitable material. Typical platedprotective coatings for mandrels include chromium, nickel, alloys ofnickel, iron, and the like. The plated metal should preferably be harderthan the metal used to form the electroform and is of an effectivethickness of for example at least 0.006 mm in thickness, and preferablyfrom about 0.008 to about 0.05 mm in thickness. The outer surface of theplated mandrel preferably is passive, i.e., abhesive, relative to themetal that is electrodeposited to prevent adhesion duringelectroforming. Other factors that may be considered when selecting themetal for plating include cost, nucleation, adhesion, oxide formationand the like. Chromium plating is a preferred material for the outermandrel surface because it has a naturally occurring oxide and surfaceresistive to the formation of a strongly adhering bond with theelectro-deposited metal such as nickel. However, other suitable metalsurfaces could be used for the mandrels. The mandrel may be plated usingany suitable electrodeposition process. Processes for plating a mandrelare known and described in the patent literature. For example, a processfor applying multiple metal platings to an aluminum mandrel is describedin U.S. Pat. Nos. 4,067,782, and 4,902,386, the disclosures of which aretotally incorporated by reference.

Articles may be formed on the mandrels of this invention by any suitableknown process, preferably electroforming. The electroformed articles maybe of any effective thickness, preferably from about 1 mm to about 2 cm,and more preferably from about 2 mm to about 20 mm. The electroformingmaterial and the electroformed articles may be of any suitable metalincluding nickel, copper, iron, steel, or aluminum.

Processes for electroforming articles on the mandrel are also well knownand described, for example, in U.S. Pat. Nos. 4,501,646 and 3,844,906,the disclosures of which are totally incorporated by reference. Theelectroforming process of this invention may be conducted in anysuitable electroforming device. For example, a plated cylindricallyshaped mandrel having an ellipsoid shaped end may be suspendedvertically in an electroplating tank. The electrically conductivemandrel plating material should be compatible with the metal platingsolution. For example, the mandrel plating may be chromium. The top edgeof the mandrel may be masked off with a suitable non-conductivematerial, such as wax to prevent deposition. The electroplating tank isfilled with a plating solution and the temperature of the platingsolution is maintained at the desired temperature such as from about 45°to about 65° C. The electroplating tank can contain an annular shapedanode basket which surrounds the mandrel and which is filled with metalchips. The anode basket is disposed in axial alignment with the mandrel.The mandrel is connected to a rotatable drive shaft driven by a motor.The drive shaft and motor may be supported by suitable support members.Either the mandrel or the support for the electroplating tank may bevertically and horizontally movable to allow the mandrel to be movedinto and out of the electroplating solution. Electroplating current suchas from about 25 to about 400 amperes per square foot can be supplied tothe electroplating tank from a suitable DC source. The positive end ofthe DC source can be connected to the anode basket and the negative endof the DC source connected to a brush and a brush/split ring arrangementon the drive shaft which supports and drives the mandrel. Theelectroplating current passes from the DC source to the anode basket, tothe plating solution, the mandrel, the drive shaft, the split ring, thebrush, and back to the DC source. In operation, the mandrel is loweredinto the electroplating tank and continuously rotated about its verticalaxis. As the mandrel rotates, a layer of electroformed metal isdeposited on its outer surface. When the layer of deposited metal hasreached the desired thickness, the mandrel is removed from theelectroplating tank.

Any suitable method and apparatus may be optionally employed to assistin the removal of the electroformed article from the mandrel. Forexample, a mechanical parabolic end parting fixture may be employed tograsp the preferably parabolic shaped end of the electroform. Thegrasping jaws may have as few as three fingers or may completely contactthe electroform circumference like a lathe collet. Alternatively, avacuum cup may be placed under the preferably parabolic shaped end ofthe mandrel. A vacuum would be generated by the use of air pressure orvacuum pump. In another approach, the electroform/mandrel compositestructure is inserted into an induction coil and by energizing the coilthe electroform is heated and consequently enlarges, thereby looseningit from the mandrel. In a different approach, vibrational energy,especially ultrasonic energy, is used to cause the electroform toseparate from the mandrel. In one embodiment, an ultrasonic bath is usedduring or after the parting gap is established to assist in removal ofthe electroform. It is also possible to use a vibrator which contactsthe electroform or the mandrel.

Other modifications of the present invention may occur to those skilledin the art based upon a reading of the present disclosure and thesemodifications are intended to be included within the scope of thepresent invention.

What is claimed is:
 1. A method for separating an electroformed articlefrom a mandrel comprising:(a) masking a portion of a mandrel with a maskcomprising an electrically nonconductive outer surface; (b)electroforming an article on the mandrel wherein the electroformingmaterial is deposited on the mandrel surface and substantially fails toadhere to or does not adhere to the nonconductive outer surface of themask, whereby the end of the electroformed article is adjacent to themask; and (c) removing the article from the mandrel by: (i) pushing themask against the end of the article to effect movement of the article inthe direction of separation; or (ii) removing the mandrel while keepingthe mask stationary, whereby the end of the article pushes against themask during withdrawal of the mandrel.
 2. The method of claim 1, whereinthe mask in step (a) is positioned around the mandrel at the top endthereof.
 3. The method of claim 1, comprising step (c)(i).
 4. The methodof claim 1, comprising step (c)(ii).
 5. The method of claim 1, whereinthe electroforming material comprises nickel, copper, iron, steel oraluminum.
 6. The method of claim 1, wherein the mandrel is fabricatedfrom nickel, copper, iron, steel, or aluminum.
 7. The method of claim 1,wherein the mask is elastic.
 8. The method of claim 1, wherein the maskcomprises a polymeric material.
 9. The method of claim 1, wherein themask comprises butyl rubber.
 10. The method of claim 1, wherein the maskhas a thickness ranging from about 2 mm to about 1 cm.
 11. The method ofclaim 1, wherein the mask has a length ranging from about 10 mm to about5 cm.
 12. The method of claim 1, wherein the coefficient of staticfriction between the mandrel surface and the mask inner surface rangesfrom about 0.05 to about
 1. 13. The method of claim 1, wherein thecoefficient of static friction between the mandrel surface and the maskinner surface ranges from about 0.05 to about 0.50.
 14. A method forseparating an electroformed article from a mandrel comprising:(a)positioning around a mandrel at the top end a mask comprising anelectrically nonconductive outer surface; (b) electroforming an articleon the mandrel wherein the electroforming material is deposited on themandrel surface and substantially fails to adhere to or does not adhereto the nonconductive outer surface of the mask, whereby the end of theelectroformed article is adjacent to the mask; and (c) removing thearticle from the mandrel by pushing the mask against the end of thearticle to effect movement of the article in the direction ofseparation.